linux-kernel - Re: [PATCH] sysfs: driver core: Fix glue dir race condition

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Date:	Fri, 7 Nov 2014 09:22:08 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	<gregkh@...uxfoundation.org>, <lizefan@...wei.com>,
	<linux-kernel@...r.kernel.org>,
	Weng Meiling <wengmeiling.weng@...wei.com>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH] sysfs: driver core: Fix glue dir race condition

On 2014/11/7 0:55, Tejun Heo wrote:
> Maybe "fix glue dir race condition by not removing them" is a better
> title?

Yes, it's better, thank you!

> 
> On Thu, Nov 06, 2014 at 04:16:38PM +0800, Yijing Wang wrote:
>> There is a race condition when removing glue directory.
>> It can be reproduced in following test:
>>
>> path 1: Add first child device
>> device_add()
>> 	get_device_parent()
>> 		/*find parent from glue_dirs.list*/
>> 		list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
>> 			if (k->parent == parent_kobj) {
>> 				kobj = kobject_get(k);
>> 				break;
>> 			}
>> 		....
>> 		class_dir_create_and_add()
>>
>> path2: Remove last child device under glue dir
>> device_del()
>> 	cleanup_device_parent()
>> 		cleanup_glue_dir()
>> 			kobject_put(glue_dir);
>>
>> If path2 has been called cleanup_glue_dir(), but not
>> call kobject_put(glue_dir), the glue dir is still
>> in parent's kset list. Meanwhile, path1 find the glue
>> dir from the glue_dirs.list. Path2 may release glue dir
>> before path1 call kobject_get(). So kernel will report
>> the warning and bug_on.
>>
>> This fix keep glue dir around once it created suggested
>> by Tejun Heo.
> 
> I think you prolly want to explain why this is okay / desired.
> e.g. list how the glue dir is used and how many of them are there and
> explain that there's no real benefit in removing them.
> 

Right, I will add the explanation. :)

> ...
>> Signed-off-by: Yijing Wang <wangyijing@...wei.com>
>> Signed-off-by: Weng Meiling <wengmeiling.weng@...wei.com>
>> Cc: <stable@...r.kernel.org> #3.4+
> 
> Except for the above nits.
> 
> Reviewed-by: Tejun Heo <tj@...nel.org>

Thanks!

> 


-- 
Thanks!
Yijing

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